Enamelling tunnel-type furnace

ABSTRACT

AN ENAMELLING TUNNEL TYPE FURNACE COMPRISING AT LEAST ONE SUPPORT MOVABLE ENTIRELY INSIDE THE CURING CHAMBER OF THE FURNACE ALONG THE LONGITUDINAL AXIS OF THE FURNACE. THE SUPPORT CARRIES THE ARTICLES TO BE HEATED. THE CURING CHAMBER IS TIGHTLY CLOSED AND BURNERS ARE FITTED INTO AT LEAST ONE OF THE WALLS OF THE CURING CHAMBER, AT A LEVEL POSITIONED ABOVE THE BASE OF SUPPORT, UNDER THE ARTICLE. AN OPENING IS PROVIDED BETWEEN THE BASE AND THE ARTICLE, SO THAT HEATING THE ARTICLES DEPOSITED ON THE SUPPORT BY CONVECTION IS POSSIBLE BY MEANS OF THE JETS OF WASTE GASES ORIGINATING FROM THE BURNERS AND DIRECTED TRANSVERSELY TO THE LONGITUDINAL AXIS OF THE CURING CHAMBER.

United States Patent [72] inventor [54] ENAMELLING TUNNEL TYPE FURNACE 14 Claims, 5 Drawing Figs.

52 u.s.c| 263/28,

263/6 [51] lnt.Cl F27b9/00 so FieldolSearch 263/28,6

[56] References Cited UNITED STATES PATENTS 1,867,772 7/1932 Smalley 263/6 2,259,741 10/1941 Drake 263/6 Primary Examiner-John J. Camby An0rneyStevens, Davis, Miller and Mosher ABSTRACT An enamelling tunnel type furnace comprising at least one support movable entirely inside the curing chamber of the furnace along the longitudinal axis of the furnace. The support carries the articles to be heated. The curing chamber is tightly closed and burners are fitted into at least one of the walls of the curing chamber, at a level positioned above the base of support, under the article. An opening is provided between the base and the article, so that heating the articles deposited on the support by convection is possible by means of the jets of waste gases originating from the burners and directed transversely to the longitudinal axis of the curing chamber.

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PATENTEU JUN28 I97! SHEET 2 BF 5 PATENTEU JUN28 19m SHEET 3 0f 5 ||||ll|||lll|ll Ill II-II lll'll llllll' ENAMELLING TUNNEL TYPE FURNACE The present invention relates to an enamelling tunnel type furnace, in particular a tunnel type furnace for enamelling bathtubs and similar articles.

Up to the present indirect heating by radiation of a muffle, of tubes or of electric resistances has been used in enamelling tunnel furnaces.

Such heating presents however many disadvantages. The quantity of heat transmitted by radiation diminishes proportionately to the square of the distance between the two surfaces between which the radiation takes place.

This results in that, inside a muffle for example, the articles or the parts of articles to 'be cured which are positioned close to the wall of the muffle will be considerably hotter than the articles or parts positioned at the center of the furnace chamber. 7

It follows moreover from the Stefan Bolzman law that, when any article is brought between the radiating surface and the article to be heated, such article will no longer be heated up on an appropriate manner. This occurs on account of the cast shadow phenomenon.

Another very serious disadvantage of heat transmission by radiation is that the thin portions of the articles are overheated compared with the thick portions.

A principle object of this invention is essentially to remove the said disadvantages and to provide a tunnel furnace by means of which it shall be possible to maintain perfect isother mal conditions around the articles to be heated, to reduce considerably the internal stresses arising when raising the tem perature of such articles, to achieve an improved transmission of the heat to the enamel of the articles to be heated and a better glassiness of the enamel.

For that purpose the enamelling tunnel furnace according to the invention comprises at least one support movable entirely inside the curing chamber of the furnace along the longitudinal axis of such furnace, upon which may be deposited the articles to be heated up. The curing chamber can be tightly closed, so as to permit the accumulation of an overpressure in the chamber. Burners opening into the curing chamber, are fitted in at least one of the walls of such chamber in such a manner that heating the articles deposited on the support by convection is possible by means of the jets of waste gases originating from the burners and directed transversely to the longitudinal axis of the curing chamber.

According to an advantageous form of embodiment of the invention the support comprises a platform sliding on rails, which run inside the curing chamber along the longitudinal axis of such chamber.

In a preferred embodiment, the furnace according to the invention comprises a trap door provided in the bottom of the curing chamber near the outlet thereof. The trap door may be closed by a vertically movable drop plate in such a manner as to permit removal of a support,after it arrives at the plate, from the curing chamber, whereby a conveyor installation is provided beneath the curing chamber, by means of which it is possible to lead the support drawn out of the curing chamber back again to the entry of the curing chamber. Gripping means are provided at the outlet of the curing chamber which make it possible to draw the articles deposited on the support carried on the plate through such outlet prior to the plate being lowered.

Further details and advantages of the invention will be hereinafter explained in connection with a particular embodiment of an enamelling tunnel type furnace according to the invention with reference to the accompanying drawings.

In the drawing: v

FIGS. 10, lb, when connected together show when connected together elevational view partially broken away, of an enamelling furnace according to the invention;

FIG. 2 shows a plan view of the arrangement according to FIG. 1a, and

FIG. 3 shows a sectional view taken along the line III-ill of FIG. 10.

In the individual FIGS. the same elements are provided with the same numerical references.

The tunnel furnace for enamelling bathtubs shown in the individual FIGS. comprises a stable welded structure 1, defining a curing chamber 2, which is subdivided in seven successive areas 3 to 9, each of which may contain a bathtub 10 deposited on a support 11, whereby the temperature of such areas may be individually adjusted.

The supports 11 are formed by platforms which slide by means of guide shoes 12 inside the chamber 2 on rails 13 extending along the longitudinal direction of the chamber. These platforms 11 are formed by two thrust tubes 14 and 15, which run parallel to the axis of the curing chamber 2 and are surrounded by very light materials 17 of high insulating capacity, whereby such materials 17 are encased with heat resisting steel sheets 16.

The bathtubs 10 are carried in cradles 18 which are mounted on the platfon'ns 11 and retain the bathtubs 10 with a minimum number of points of contact in the direction of the axis of the curing chamber 2.

Burners 19 opening into the curing chamber 2 are mounted in the sidewall 27 of the chamber at a level positioned between the platfonns 11 and the bathtubs 10 in such a manner as to permit the establishment of a circulation of combustion gases around such bathtubs 10. The gases originate from the burners 19, so that by such means, and also because of the shape of the chamber 2, a maximum transmission of heat by convection of such gases to the bathtubs carried in the cradles 18 will take place.

The burners 19 are fed with an air-gas mixture in stoichiometric ratios together with an additional slight excess of air in such a manner as to obtain complete burned gases inside the curing chamber 2. The burners l9 emit jets of gas with a velocity of m. per sec. magnitude and these jets draw, by reason of the injector effect, the gases from the curing chamber 2 surrounding them along in the direction of the arrows 40, so as to establish by such means a vortex inside the curing chamber in the direction of the arrows 41 (see FIG. 3). This favors the transmission of heat by convection, as this is proportionate to the velocity of the gases in contacting relationship with the articles to be heated.

A trap door 21 is provided in the bottom of the curing chamber 2 within the area 9 thereof. This trap door 21 is closed by a vertically movable drop plate 23 in such a manner as to make it possible to lead the platform 11 pushed on plate 23 out of the chamber 2 at the end of the curing operation and to bring it at the level of a conveyor installation 42 mounted inside a pit 22 beneath the curing chamber 2. The conveyor 42 assures the return of the empty platforms 11 led out of the curing chamber 2 through the trap door 21 back to the inlet of the chamber 2. At the outlet 24 of the curing chamber 2 are provided gripping means, not shown in the FIGS. formed by an automatic discharge device. By means of such gripping devices it is possible to lead the cured bathtubs 10 through the outlet 24 at the moment when the platform 11 is positioned above the trap door 21 and prior to lowering plate 23.

The drop plate 23 is mounted on supports 20 laid out in a scissors like arrangement, whereby the mutual distance of these supports is controlled by hydraulic jacks 28 in such a manner as to permit raising and lowering the plate 23 between the trap door 21 and the conveyor 42. The conveyor comprises two endless chains 43 and 44, each of which moves in vertical planes on either side of the plate 23 in the lowered position between the plate 23 and the inlet 25 of the curing chamber 2. A transverse thrust rod 45 is provided between the two chains 43 and 44 and assures, by acting on the rear rim of the platform 11 positioned on the plate 23 in the lowered position, the sliding of such platform from the plate 23 on to rails 46, which extend between the chains 43 and 44 as far as the inlet of the curing chamber 2.

The plate 25 is also provided with rails 47 which, in the raised position of the plate, are located in the extension of rails 70 which run inside the curing chamber 2 and, in the lowered position of the plate 23, provide an extension for the rails 46 of the conveyor 42.

An elevator plate 48 is provided at the inlet 25 of the curing chamber 2. This elevator plate 48 permits raising an empty platform 11, withdrawn from the curing chamber 2 and led back by the conveyor 42 beneath the inlet 25 of the chamber 2, to the level of such inlet 25, in such a manner that such platform 11, loaded with a new bathtub may be introduced anew in the area 3 of the curing chamber 2. This elevator plate 48 is of the same type as the drop plate 23 and is likewise controlled by means of hydraulic jacks 28 actuating crossed scissorlike supports beneath the plate 48, in such a manner as to permit the raising and lowering thereof between the conveyor 42 and the inlet of the curing chamber 2.

The elevator plate 48 is actuated by means of a driving device 49 which imparts a reciprocal motion to such plate 48 corresponding to the direction of movement of the chains 43 and 44 between a position removed from and another close to the conveyor 42. The movements of the elevator plate 48 and of the conveyor 42 are synchronized in such a manner that the empty platform 11 may be moved on the one hand from the rails 46 of the conveyor 42 onto the rails 50 of the elevator plate 48. At the moment when the latter is in the lowered position shown in chain dotted lines in FIG. 1a, with is in the position close to the conveyor 42 the thrust rod 45 may pass between the ends of the rails 46 of the conveyor 42 and the plate 48 at the moment when the latter is in the position removed from the conveyor 42.

When the elevator plate 48 is in the position close to the conveyor 42, the rails 50 are arranged in the extension of the rails 46.

The said driving device 49 comprises a connecting rodcrank system 54 articulated on a chassis 51 carrying the supports 20 and the plate 48. The chassis 51 is provided with rollers 52 running on rails 53 in such a manner that a reciprocal motion may be imparted to the chassis resulting from the action of the connecting rod-crank system 54.

A thrust device 55 is provided facing the inlet of the curing chamber 2. This device 55 may actuate a platform 11, positioned on the elevator plate 48 when the latter is in the raised position, in such a manner that this platform 11 is advanced inside the curing chamber 2.

The thrust device 55 is guided on either side of the elevator plate 48 on rails 56 running parallel to the longitudinal axis of the curing chamber 2. A carriage 57, actuated by a connecting rod-crank system 58, able to move on such rails 56, slightly above the elevator plate 48, when in the raised position and to push a platform 11, positioned on the said plate 48, inside the curing chamber 2.

The connecting rod-crank system 58 actuates a shaft 59 provided at each of the ends thereof with a pinion 60 which meshes, on the one hand, in the lower portion thereof, with a stationary toothed rack mounted on the rails 56 parallel to the axis of the curing chamber 2 and, on the other hand, in the upper portion thereof, with a toothed rack 61, which is mounted on the carriage 57 in such a manner that the travelling speed of the carriage 57 shall be twice the travelling speed of the pinions 60.

The outlet door 31 is actuated by means of an eccentric 35 in such a manner as to permit the fast closing and opening of the door, thus reducing the admission of air to a minimum.

The inlet 25 of the curing chamber 2 is likewise provided with a door 64 able to open at the moment when the elevator plate 48 takes up the position removed from the conveyor 42. This door 44 opens in a downward direction, as does indeed also the outlet door 31, in order to engage between the plate 23 and the conveyor 42.

Because the curing chamber 2 of this invention is completely leakproof in a section at right angles to the longitudinal axis of the chamber 2, it is possible to achieve in such chamber a very forceful convection heating by means of a stream of waste gases flowing substantially in a transverse direction to the longitudinal axis of the chamber 2. Since the velocity of such gases produces kinetic pressures on the walls of the curing chamber 2, such leak tightness is indeed absolutely necessary.

Another problem which has been solved by the furnace according to the invention is to prevent that a very hot bathtub 10 and a very hot support 11 are delivered at the outlet 24 of the curing chamber 2, whereby the support 11, very difficult to handle because of the size, weight and high temperature thereof, has to be brought back to the inlet of the curing chamber 2. For this purpose the bathtub 10 and the support 11 are withdrawn separately from the curing chamber 2 through two different outlets.

A first stack 29 for removing the waste gases, which circulate in the opposite direction to that of the advance of the bathtubs 10, is connected with area 3 of the curing chamber 2, located close to the inlet 25, while a second stack 30 is provided in the door jambs of the outlet 24 ofthe chamber 2. This second stack 30 is only opened during the opening of the trap door 21 and of the door 32 provided at the outlet 24 of the curing chamber 2, whereby the first stack 29 is closed in that case. By this means, the air which enters through'the door 31 and through the trap door 21 is exhausted by the stack 30, while the gases originating from the burners 19 and which are unable to escape through the stack 29 prevent air from entering the areas 3 to 8 of the curing chamber 2. Such gases are then exhausted with the air by means of the stack 30. The existence ofthe stack 30 makes it possible to maintain in the curing chamber 2 a mixture determined from experience which contains between 0.5 and L5 percent oxygen. I

The areas 3 and 4 of the curing chamber, located close to the stack 29 are not fitted in the present case with burners 19 and provide heat recovery zones. The gases of combustion of the other areas 5 to 9 circulate here in a direction contrary to that of the advance of the bathtubs l0 and escape through the stack 29.

ln order to establish in such areas 3 and 4 a transverse circulation of the waste gases, i.e. in order to subject the waste gases to a vortex motion along the axis of the curing chamber 2, injector runs 33 are provided in the wall 27 of the curing chamber 2.

These injectors or injection nozzles 33 are fed by a motor fan 34, which draws a portion of the waste gases from the curing chamber 2 through pipes 63 and which compresses these gases to the required pressure, in order that at the outlet of the injectors 33 they shall have sufficient kinetic ,energy to establish the transverse circulation in the areas 3 and 4. This circulation is established automatically in the other areas 5 to 9 by the burners 19 themselves.

It is likewise possible to provide in the areas 5 to 9 injectors 33 in such a manner that when the burners 19 are idling or stopped, the necessary circulation of the waste gases nevertheless takes place. This last case may occur, for example, when the heating program of the bathtubs 10 does not call for a heat supply in a specific area.

The tunnel furnace hereinbefore described, wherein the mass enamel, applied to the bathtubs 10 by spraying or immersion, is cured, operates as follows:

Under normal conditions the furnace chamber 2 comprises in each of the areas 3 to 9 a platform 11, which carries a bathtub 10 in cradles 18. The thrust tubes 14 and 15 of the platforms 11 are positioned end to end in such a manner as to permit moving the platforms from one area to another by pushing the platform 11 positioned in the first area. When a bathtub 10 reaches area 9, above the trap door 21, then the curing of such bathtub is terminated, the door 31 opens and the bathtub 10 is withdrawn through the outlet 24 by means of an automatic discharge device. Prior to the opening of the door 24, the stack 29 is closed and the stack 30 opened.

Subsequently the plate 23 is lowered and thereby withdraws the empty platform 11 from the curing chamber 2. When the plate 23 reaches its lowered position, as shown in chain dotted lines in FIG. 10, the rails 47 of the plate are positioned in the extension of the rails 46 and the platform 11 is pushed by the rod 45 on to such rails 46.

The plate 23 closes again the trap door 21 in such a manner that the thrust device 55 may push the bathtubs in the curing chamber by one step, i.e. may move each of the bathtubs to the next following area, so as to permit the introduction of a platform 11 with a new bathtub in the first area 3.

After the elevator plate shall have been thus discharged, it is brought after closure of the inlet door 25 to its lowered position close to the conveyor 42.

The rod 45 thereupon pushes the empty platform 11 onto the elevator plate 48 which raises the former until it faces the inlet 25 of the curing chamber 2.

At that moment a new bathtub 10 may be deposited in the cradlelike structures 18 of the platform, which rests on the elevator plate 48 in such a manner as to permit starting a new cycle.

Limit switches, not shown, assure the safety of the different operations.

It is well understood that the invention is not limited to the described form of embodiment and that many changes may be introduced therein without departing from the scope of the present patent application as defined in the following claims.

I claim:

1. An enamelling tunnel type furnace, in particular a tunnel type furnace for enamelling bathtubs, comprising at least one support movable entirely inside the curing chamber of the furnace along the longitudinal axis of such furnace, upon which may be deposited the articles to be heated, means to tightly close the curing chamber so as to permit the accumulation of an overpressure, burners opening into the curing chamber and fitted in at least one of the walls of the curing chamber, at a level positioned above the base of the supports and under said articles, an opening being provided between the base and the articles, so that heating of the articles on the support by convection is possible by means of the jets of waste gases originating from the burners and directed transversely to the longitudinal axis of the curing chamber.

2. A furnace as claimed in claim 1, wherein the base of the support has a platform sliding on rails, which run inside the curing chamber along the longitudinal axis of such chamber.

3. A furnace as claimed in claim 1 including a trap door in the bottom of the curing chamber near the outlet of said chamber said trap door being closed by means of a vertically movable drop plate in such a manner as to permit drawing the support arriving at said plate out of the chamber, whereby a conveyor installation is provided beneath the curing chamber, by means of which it is possible to lead the support drawn out of the curing chamber back again to the entry of the curing chamber.

4. A furnace as claimed in claim 3, wherein a lifting device is provided at the inlet to the curing chamber, such device permitting to raising of the empty support withdrawn from the curing chamber and led back by means of the conveyor to the inlet of the furnace chamber to the inlet level in such a manner that, after loading thereof with articles to be heated, such support may again be introduced in the curing chamber.

5. A furnace as claimed in claim 3, wherein the conveyor comprises two endless chains or belts which run in vertical planes on either side of the plate in the lowered position between such plate and the inlet of the curing chamber, a rod being mounted between the two chains or belts which may be pushed over the plate in the lowered position position in such a manner that it is possible to move a support positioned on such plate to the inlet of the curing chamber.

6. A furnace as claimed in claim 4, wherein means for actuating the lifting device are provided which enables a reciprocal motion to be imparted to the latter between a position the lowered position and, on the other hand, the passage of the conveyor members is made possible at the moment when the liftingdevice is removed from the conve or.

7. furnace as claimed l1l claim 4, w ereln a thrust device is provided facing the inlet of the curing chamber and such device may actuate a support positioned on the lifting device in the raised position thereof in such a manner that the support is advanced inside the curing chamber.

8. A furnace as claimed in claim 7, wherein the thrust device guided on either side of the lifting device on rails parallel to the longitudinal axis of the curing chamber is provided with a carriage actuated by a connecting rod-crank system, such carriage being movable on such rails above the lifting device and may act by means of push rods on a support mounted on the lifting device in the raised position in such a manner as to advance the support inside the curing chamber.

9. A furnace as claimed in claim 8, wherein the connecting rod-crank system actuates a shaft provided at each of the ends thereof with a pinion, such pinion meshing, on the one hand in the lower portion thereof with a stationary toothed rack, mounted on the guide rails parallel to the axis of the curing chamber and, on the other hand, in the upper portion thereof with a toothed rack mounted on the carriage running on the guide rails and this in such a manner that the travelling speed of the carriage shall be twice that of the pinions.

10. A furnace as claimed in claim 1, wherein the support is provided with at least one cradle like structure, which is used to carry the articles to be heated with a minimum number of points of contact and is mounted substantially in the direction of the axis of the curing chamber, so that the gases of combustion may flow along the surfaces of the articles to be heated.

11. A furnace as claimed in claim 1, wherein to exhaust the gases of combustion a first stack connected with an area of the curing chamber located close to the inlet of the curing chamber and to exhaust the air admitted on opening the outlet of the curing chamber a second stack is provided, the latter being connected with an area of the chamber located close to the outlet of the curing chamber, means to close and to open such second stack simultaneously with the outlet of the curing chamber, so that when the first stack is closed, the second stack is open and the first stack is open when the second stack is closed.

12. A furnace as claimed in claim 1, wherein the curing chamber is provided close to the inlet thereof with a heat recovery zone, such zone not being fitted with burners, the gases of combustion originating from other areas flowing therethrough in a direction contrary to that of the movement of the support.

13. A furnace as claimed in claim 1, wherein at least one injector is mounted in one of the walls of the curing chamber at least in the area close to the inlet of such chamber, such injector being fed by a fan, which draws gases from the curing chamber and produces a gas flow transversely to the longitudinal axis of such chamber.

14. A furnace as claimed in claim 1, wherein the burners open into the curing chamber at a level which is located between that of the support and that of the article or articles positioned thereon, so that a circulation of the gases of combustion is assured around the article or articles. 

